Generally, a magnetic sensor has been widely used for a current detection element and a position detection element for example. In recent years, more magnetic sensors have a higher accuracy and have higher requirements for magnetic sensor characteristics (sensitivity and an offset voltage) regarding a reduced variation. Generally, a characteristic is adjusted on a sensor module circuit on which a magnetic sensor is mounted based on the variable resistance for example. If the variation among magnetic sensors can be reduced on wafers, a step of adjusting the individual magnetic sensors on circuits is eliminated, thus realizing a lower cost as well as a smaller size and a lighter weight.
FIG. 1A and FIG. 1B are a configuration diagram illustrating a conventional magnetic sensor. FIG. 1A is top view. FIG. 1B is a cross-sectional view taken along the line IB-IB′ in FIG. 1A. FIG. 2 is a circuit diagram illustrating the equivalent circuit of FIG. 1A. In the drawings, the reference numeral 1 denotes a magnetic sensitive portion, the reference numerals 1a and 1b denote an input terminal of a magnetic sensitive portion, the reference numerals 1c and 1d denote an output terminal of a magnetic sensitive portion, the reference numeral 2 denotes a bonding electrode pad, the reference numeral 5 denotes a protection layer, and the reference numeral 6 denotes a substrate.
A conventional magnetic sensor is structured, as shown in FIG. 1A and FIG. 1B, so that a substrate 6 has thereon a magnetic sensitive portion 1 that is composed of a compound semiconductor and that has a cross-shaped pattern. This magnetic sensitive portion 1 constitutes a bridge circuit as shown in FIG. 2. The magnetic sensitive portion 1 includes input terminals 1a and 1b and output terminals 1c and 1d. These input terminals 1a and 1b and output terminals 1c and 1d are connected to bonding electrode pads 2, respectively. The magnetic sensitive portion 1 has thereon a protection layer 5.
The conventional magnetic sensor having the configuration as described above does not have a trimming portion. Thus, as shown in FIG. 2, the constant voltage Vin is directly applied between the input terminals 1a and 1b of the magnetic sensitive portion 1. A constant voltage sensitivity of a magnetic sensor is determined depending on a compound semiconductor mobility and the shape of the magnetic sensitive portion 1 (a ratio between the length and the width) and the constant voltage Vin. This means that the semiconductor layer mobility and the variation in the magnetic sensitive portion shape between elements (between a wafer plane and the wafer) directly result in the variation in the constant voltage sensitivity, thus failing to adjust the constant voltage sensitivity.
Among methods for reducing the variation in the magnetic sensor characteristic as described above, a method is known as disclosed in Patent Documents 1 and 2 for example to trim the magnetic sensor. The method disclosed in Patent Document 1 relates to a Hall element having a small unbalanced voltage according to which, while measuring a voltage between Hall voltage terminals, a slit of a required amount is provided in the Hall voltage terminal and an attachment section and a method is used to subject the magnetic sensitive portion to metal plating. By the method as described above, the offset voltage is adjusted.
FIG. 3 is a circuit diagram illustrating an equivalent circuit of the above-described magnetic sensor disclosed in Patent Document 1. In FIG. 3, the reference numerals 11a and 11b denote an input terminal of a magnetic sensitive portion, and the reference numerals 11c and 11d denote an output terminal of a magnetic sensitive portion. This Patent Document 1 discloses that the magnetic sensitive portion can be trimmed to adjust the offset voltage. However, the constant voltage sensitivity cannot be adjusted since the voltage Vin applied to the magnetic sensitive portion (bridge circuit) is constant, the constant voltage sensitivity.
The method disclosed in Patent Document 2 relates to a magnetic sensor used for a speed sensor or a magnetic encoder according to which a resistor body constituting a bridge in a magnetic resistive element is trimmed by being subjected to laser irradiation to thereby adjust the offset voltage.
As described above, in the case of any of the above-described methods disclosed in Patent Document 1 and 2, the offset voltage can be adjusted on the wafer. However, these conventional methods could not adjust the sensitivity.
The present invention has been made in view of the above disadvantage. It is an objective of the present invention to provide a magnetic sensor for which the sensitivity can be adjusted on a wafer, the mass-productiveness is superior, and the characteristic variation is small.